Activity series and smart tasks

I am trying to create some activity series, but I want to also be able to link it to some smart tasks that I have created. The idea is that on completion of a certain stage of the activity series, a Smart task will run and then the activity series will continue.

Also, is there a way to create an activity series that can call other activity series, or that can be set to have different activities run based on the results of a previous activity?